The Browning Automatic Rifle model of 1918 is used by gretle in the anime.
History and use
The Browning Automatic Rifle (BAR) was a family of United States automatic rifles (or machine rifles) and light machine guns used by the United States and numerous other countries during the 20th century. The primary variant of the BAR series was the M1918, chambered for the .30-06 Springfield rifle cartridge and designed by John Browning in 1917 for the U.S. Expeditionary Corps in Europe as a replacement for the French-made Chauchat and M1909 Benet-Mercie machine guns.
The BAR was designed to be carried by advancing infantrymen, slung over the shoulder or fired from the hip, a concept called "walking fire"—thought to be necessary for the individual soldier during trench warfare. However in practice, it was most often used as a light machine gun and fired from a bipod (introduced in later models). A variant of the original M1918 BAR, the Colt Monitor Machine Rifle, remains the lightest production automatic gun to fire the .30-06 Springfield cartridge, though the limited capacity of its standard 20-round magazine tended to hamper its utility in that role.
Although the weapon did see some action in World War I, the BAR did not become standard issue in the U.S. Army until 1938 when it was issued to squads as a portable light machine gun. The BAR saw extensive service in both World War II and the Korean War and saw some service early in the Vietnam War. The U.S. Army began phasing out the BAR in the late 1950s and was without a portable light machine gun until the introduction of the M249 Squad Automatic Weapon in the mid-1980s. 
In the anime
In the anime, it is seen to be taller then gretle and has an unlimited ammo mag in it.
- the gun is 18-22lbs
- it only has 20rds in the gun
- the 30.06 round it shoots is large with plenty of recoil
- you can not carry the amount of ammo that is on the floor of the bar alone
- Bonie parker was 90lbs and could shoot it better then most men so it can be fired from someone with a small frame